DEXTRAN AND HYDROXYETHYL STARCH INTERFERE WITH FIBRINOGEN ASSAYS

We studied the haemostatic and volume effects of synthetic plasma subs titutes and Ringer's solution in 48 surgical patients and found that t he measured fibrinogen concentrations of patients receiving either dex tran or hydroxyethyl starch (HES) were significantly higher than those predicted by the dilutional effects. The groups given Ringer's soluti on showed no apparent disproportion between fibrinogen concentration a nd plasma volume change. The results suggested that the presence of ar tificial colloids might interfere with the indirect fibrinogen assay u sed in the study. The method of analysis was based on light scattered from the reaction mixture during prothrombin time (PT) measurement. To test the hypothesis, plasma was obtained from nine volunteers to prep are 20, 40 and 60% dilutions in normal saline, 6% dextran 70, 6% HES 1 20/0.7 or 6% HES 200/0.5 solutions. Fibrinogen was measured on a ACL-3 00R coagulometer by two indirect methods, PT derived and the Clauss me thod. Relative concentrations were compared by analysis of variance an d Sheffe's multiple comparisons. Dilutions containing either dextran o r HES gave significantly higher values (P < 0.001) than samples dilute d with normal saline. We conclude that the results of indirect fibrino gen assays should be interpreted cautiously; when HES or dextran is us ed for volume replacement. This may be particularly true when hypofibr inogenaemia is encountered after extensive use of synthetic colloids d uring massive transfusion.